Widespread use of antibiotics in recent decades has led to proliferation of pathogens having multiple drug resistance, often encoded by transmissible plasmids, and therefore capable of spreading rapidly between species. Many previously useful antibiotics are no longer effective against infectious organisms isolated from human and animal subjects. The specter of epidemic forms of bacterial diseases such as tuberculosis and fungal diseases, which are refractory to known antibiotic agents, may be realized in the near future. Development of novel antimicrobial compounds is a continuing urgent public health need.